Abstract

Objective: The administration of amino acid (AA) mixtures that are selectively deficient either in tryptophan or phenylalanine plus tyrosine can decrease serotonin or catecholamine synthesis, respectively. In the present study, we assessed whether a mixture that was simultaneously deficient in tryptophan, phenylalanine and tyrosine could induce sufficient protein synthesis that plasma levels of all 3 monoamine precursors would decrease.

Results: The tryptophan/phenylalanine/ tyrosine-deficient mixture lowered plasma concentrations of the 3 AAs by 67%, 78% and 77%, respectively (p ≤ 0.001); their ratio to other large neutral AAs was decreased more, namely, by 87%, 90% and 90% (p ≤ 0.001). Mood lowering was seen on 3 subscales of the bipolar Profile of Mood States, that is, elated–depressed, composed–anxious and clearheaded–confused, as well as 2 visual analog scales, bored and irritated (p ≤ 0.05).

Conclusions: Acute tryptophan/phenylalanine/tyrosine depletion may be a suitable new method for rapidly decreasing serotonin and catecholamine transmission simultaneously.

Acknowledgements: The authors are grateful to Ms. Francine Weston and Ms. Franceen Lenoff for their expert assistance. Drs. Leyton and Benkelfat are the recipients of salary awards from Fonds de la recherche en santé du Québec (FRSQ).

Competing interests: None declared.

A preliminary report based on this study was presented at the 25th annual meeting of the Canadian College of Neuropsychopharmacology, 9–12 June 2002, Ottawa, Ont.